Housing for an electric motor

ABSTRACT

An electric motor includes a housing with a tubular wall extending in an axial direction of the housing and a closures positioned at opposite axial ends of the tubular wall, a stator fixedly mounted inside of the housing, a rotor rotatably mounted inside of the housing, and a bearing rotatably supporting the rotor. At least one of the closures includes a rotor supporting portion. The rotor supporting portion includes a through hole configured to receive a portion of the rotor. The through hole is defined by a closed shape including at least three or more straight sides, and a radius of an inscribed circle of the closed shape of the through hole is larger than a radius of the portion of the rotor received in the through hole.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation of U.S. application Ser. No. 17/564,380, whichwas filed on Dec. 29, 2021, which is a Continuation of U.S. applicationSer. No. 16/484,127, which was filed on Aug. 7, 2019 as a U.S. nationalstage of PCT Application No. PCT/JP2018/008789, filed on Mar. 7, 2018,and with priority under 35 U.S.C. § 119(a) and 35 U.S.C. § 365(b) beingclaimed from German Application No. 102017104892.8, filed Mar. 8, 2017,the entire disclosures of each application are hereby incorporatedherein by reference.

FIELD OF THE INVENTION

Various example embodiments relate generally to a housing for anelectric motor.

BACKGROUND

Electric motors have gained significant importance in driving systemsemployed in mobile environments such as in vehicles. In driving systemsof this kind, the volume of an electric motor is a key parameter that issubject to permanent optimization. The volumes of electric motors aredetermined inter alia by their housings.

SUMMARY

In view of the above, example embodiments of the present disclosureprovide housings for electric motors each having a compact structure.

According to an example embodiment of the present disclosure, anelectric motor includes a housing including a tubular wall extending inan axial direction of the housing and closures positioned at oppositeaxial ends of the tubular wall, a stator fixedly mounted inside of thehousing, a rotor rotatably mounted inside of the housing, a bearingrotatably supporting the rotor, wherein at least one of the closuresincludes a rotor supporting portion that includes a through hole toreceive a portion of the rotor, the through hole is defined by a closedshape including at least three or more straight sides, and a radius ofan inscribed circle of the closed shape of the through hole is largerthan a radius of the portion of the rotor received in the through hole.

The above and other elements, features, steps, characteristics andadvantages of the present disclosure will become more apparent from thefollowing detailed description of the example embodiments with referenceto the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of a housing for an electric motoraccording to a first example embodiment of the present disclosure.

FIG. 2 shows a schematic view of a housing for an electric motoraccording to a second example embodiment of the present disclosure.

FIG. 3 shows a schematic view of a housing for an electric motoraccording to a third example embodiment of the present disclosure.

FIG. 4 shows a schematic view of a housing for an electric motoraccording to a fourth example embodiment of the present disclosure.

FIG. 5 shows an enlarged sectional view of a portion of a tubular wallof a housing for an electric motor.

FIG. 6 is a top view of the housing shown in FIG. 1 .

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawingsthat show, by way of illustration, specific details and exampleembodiments in which the disclosure may be practiced.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration”. Any example embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other example embodiments or designs.

FIG. 1 shows an exemplary housing 100 for an electric motor according toa first example embodiment of the present disclosure. The housing 100includes: a tubular wall 102 extending in an axial direction A of thehousing 100, and closures 104, 106 respectively positioned at oppositeaxial ends 102 a, 102 b of the tubular wall 102 and configured torotatably support respective opposite axial end portions 108 a, 108 b ofa rotor 108, e.g., by means of respective bearings 110 a, 110 b. One ofthe closures 104 is formed separately from the tubular wall 102 andincludes a radially inner portion 112 and a radially outer flange 114that, in an assembled state, is in physical contact with a radiallyinner surface 116 of the tubular wall 102 and extends from the radiallyinner portion 112 of the separately formed closure 104 towards theopposite axial end 102 b of the tubular wall 102.

In a housing 100 according to the present disclosure, the space in theinterior of the tubular wall 102 occupied by the separately formedclosure 104 is minimized, since the flange 114 extends from the radiallyinner portion 112 towards the opposite axial end 102 b of the tubularwall 102. In this way, the space 118 surrounded by the flange 114 of theseparately formed closure 104 and delimited by the radially innerportion 112 of the separately formed closure 104 is open to the interiorspace 120 defined by the tubular wall 102 and may be, hence, utilizedfor accommodating parts of an electric motor such as wiring or at leasta part of an electronic circuits (not shown in the figures). In thisway, the interior space 120 defined by the tubular wall 102 may beefficiently utilized. Consequently, a compact housing 100 may beprovided in this way.

In the example embodiment shown in FIG. 1 , only one closure 104 isformed separately from the tubular wall 102, while the other closure 106is formed integrally with the tubular wall 102. However, it isunderstood that both closures 104, 106 may be formed separately from thetubular wall 102.

The separately formed closure 104 may be press fit into the interior ofthe tubular wall 102. In this way, no additional coupling means arerequired providing a housing 100 with a simple overall setup.

The axial end 102 a of the tubular wall 102 configured to receive theseparately formed closure 104 therein may have an inner diameter thatincreases with increasing axial distance form the opposite axial end 102b. In this way, the separately formed closure 104 may be easily insertedinto the tubular wall 102 and brought into press fit engagement with theradially inner surface 116 of the tubular wall 102. Alternatively oradditionally, the separately formed closure 104 may have an outerdiameter that increases with increasing axial distance from its radiallyinner portion 112, i.e. with decreasing distance from the integrallyformed closure 106 in the assembled state of the separately formedclosure 104. This specific configuration can be achieved bymanufacturing the separately formed closure 104 by press forming or deepdrawing. The increasing outer diameter of the separately formed closure104 may be a result of intrinsic resilient forces of the material of theseparately formed closure 104. The tubular wall 102 may also be formedby press forming or deep drawing.

By means of the above configuration, the flange 114 of the separatelyformed closure 104 may be formed with an outer diameter, at least at itsaxial end opposite to its end connected to the radially inner portion112, that is larger than an inner diameter of an axial portion of thetubular wall 102 in a state in which the separately formed closure 104is separated from the tubular wall 102. In this way, the separatelyformed closure 104 can be securely fixed to the tubular wall 102. Morespecifically, a high static frictional force can be provided between anouter circumferential edge of the flange 114 of the separately formedclosure 104 and the tubular wall 102 when the separately formed closure104 is inserted into the tubular wall 102 as shown in FIG. 1 .

Hence, by means of a such configured tubular wall 102 and/or separatelyformed closure 104, a high force can be exerted between the separatelyformed closure 104 and the inner surface 116 of the tubular wall 102 inthe assembled state of the separately formed closure 104, in particularin case of small contact areas. Consequently, the flange 114 of theseparately formed closure 104 may be provided with small axialdimensions, meaning that in the mounted state, the separately formedclosure 104 occupies little space in the interior of the tubular wall102. In this way, the housing 100 may be provided with small dimensionsin the axial direction A and, hence, with a compact structure.

As indicated in FIG. 1 , the radially inner portion 112 of theseparately formed closure 104 may include a rotor supporting portion 122configured to rotatably support the axial end portion 108 a of the rotor108 by means of the bearing 110 a. The rotor supporting portion 122 mayinclude an annularly shaped circumferential wall 124 extending in theaxial direction A of the housing 100 and configured to receive thebearing 110 a therein for rotatably supporting the axial end portion 108a of the rotor 108. The annularly shaped circumferential wall 124 may beintegrally connected to the flange 114 by means of a connection portion126 of the radially inner portion 112. In the example embodiment shownin FIG. 1 , the connection portion 126 extends substantially in theradial direction of the housing 100.

As shown in FIG. 1 , the circumferential wall 124 may be in theassembled state of the separately formed closure 104 substantiallyparallel to the flange 114 and may extend from the connection portion126 towards the opposite axial end 102 b of the tubular wall 102. Bymeans of a circumferential wall 124 of this kind, a radial force may beexerted onto the bearing 110 a in the assembled state of the separatelyformed closure 104. Consequently, the bearing 110 may be press fit intothe rotor supporting portion 122, meaning that no additional fixingmeans are required.

The rotor supporting portion 122 of the separately formed closure 104may include an axial end wall 128 including a through hole 130 extendingin the axial direction A and configured to receive the rotor 108therein. The axial end wall 128 may be formed at an axial end of thecircumferential wall 124 facing the respective other closure 106, i.e.the integrally formed closure 106 in the example embodiment shown inFIG. 1 . The axial end wall 128 of the rotor supporting portion 122 mayserve as a positioner for positioning the bearing 110 a in the axialdirection A.

As shown in FIG. 1 , a bearing insertion opening 132 may be formed at anaxial end of the circumferential wall 124 opposite to the axial end wall128 of the rotor supporting portion 122. By means of this configuration,the bearing insertion opening 132 is visible from the exterior of thehousing 100, i.e. the bearing 110 a may be easily inserted into therotor supporting portion 122.

The integrally formed closure 106 may include a rotor supporting portion134 configured to rotatably support an axial end portion 108 b of therotor 108 by means of a bearing 110 b. The rotor supporting portion 134of the integrally formed closure 106 may also include an annularlyshaped circumferential wall 136 extending in the axial direction A andconfigured to receive the respective bearing 110 b therein for rotatablysupporting the respective axial end portion 108 b of the rotor 108.

The circumferential wall 136 of the rotor supporting portion 134 of theintegrally formed closure 106 may be provided with an axial end wall 138at an axial end thereof facing the separately formed closure 104. Theaxial end wall 138 may be provided with a through hole 140 extending inthe axial direction A and configured to receive the rotor 108 therein.

As shown in FIG. 1 , a bearing insertion opening 142 may be formed at anaxial end of the circumferential wall 136 opposite to the axial end wall138 of the rotor supporting portion 134. By means of this configuration,the bearing insertion opening 142 is visible from the exterior of thehousing 100, i.e. the bearing 110 b may be easily inserted into therotor supporting portion 134.

As indicated in FIG. 5 , the radially inner surface 116 of the tubularwall 102 may include a positioner 117 configured to be brought intophysical contact with the flange 114 of the separately formed closure104. The positioner 117 may, hence, serve as a positioner forpositioning the separately formed closure 104 in a defined axialposition in the interior of the tubular wall 102.

In the example embodiment shown in FIG. 5 , the positioner 117 may beconfigured as a step extending in the circumferential direction of thetubular wall 102 and protruding radially inwardly with respect to theaxial end 102 a of the tubular wall 102 configured to receive theseparately formed closure 104. The step 117 may continuously extend inthe circumferential direction of the tubular wall 102. By means of apositioner 117 of this kind, the entire circumference of the separatelyformed closure 104 may be positioned in the interior of the tubular wall102 in a well-defined axial position.

The through hole 130 of the separately formed closure 104 and/or thethrough hole 140 of the integrally formed closure 106 may be providedwith a non-rotationally symmetric shape such as a triangular orpolygonal shape. Due to the non-rotationally symmetric shape of thethrough hole 130 of the separately formed closure 104 and/or the throughhole 140 of the integrally formed closure 106, one or both axial endportions 108 a, 108 b of the rotor 108 can be held substantially at thecenter of the respective through holes 130, 140 even before insertingthe bearing 110 a into the bearing insertion opening 132 of theseparately formed closure 104 and/or the bearing 110 b into the bearinginsertion opening 142 of the integrally formed closure 106. In this way,the bearings 110 a and 110 b can be mounted independently of one anotherinto the respective bearing insertion openings 132, 142 of theseparately formed closure 104 and the integrally formed closure 106,respectively, and onto the opposite axial end portions 108 a, 108 b ofthe rotor 108. This in turn offers the opportunity of measuring forcesoccurring during the assembly of a bearing 110 a, 110 b onto an axialend 108 a, 108 b of the rotor 108 independently of the respective otherbearing 110 a, 110 b and, hence, very precisely in order to prevent,e.g., a plastic deformation of the housing 100 during assembly caused byexcessive forces exerted thereon. An independent measurement of forcesis not possible in case the bearings 110 a, 110 b are mounted onto theopposite axial ends of the rotor 108 simultaneously which would benecessary, if none of the through holes 130, 140 was provided with anon-rotationally symmetric shape. Consequently, due to thenon-rotationally shape of the through hole 130 of the separately formedclosure 104 and/or of the through hole 140 of the integrally formedclosure 106, the assembly of the rotor 108 into the housing 100 can beperformed in a simple way, since no further means are required forkeeping the rotor 108 in a central position with respect to the tubularwall 102 during assembly.

A top view of the separately formed closure 104 is shown in FIG. 6 . Forreasons of simplicity, the bearing 110 a is omitted in FIG. 6 .

As shown in this figure, the through hole 130 may be provided with theshape of an isosceles triangle configured to receive the rotor 108therein, meaning that the radius of the inscribed circle of thetriangular through hole 130 is slightly larger than the radius of theportion of the rotor 108 received in the through hole 130.

A through hole with a non-rotationally symmetric shape may also serve asa positioner, e.g., for positioning the respective closure in a definedrotational position on a production band. In this way, the closures 104,106 or the closures 104, 106 and the tubular wall 102 may be machined atdefined and/or mutually corresponding positions in the circumferentialdirection.

In FIG. 2 , a housing for an electric motor according to a secondexample embodiment is shown. The second example embodiment will bedescribed only inasmuch as it differs from the first example embodimentshown in FIG. 1 . In FIG. 2 , parts corresponding to parts of thehousing 100 shown in FIG. 1 will be denoted by the same referencenumerals, however, enhanced by the number 100.

The exemplary housing 200 according to the second example embodimentdiffers from the housing 100 shown in FIG. 1 in view of theconfiguration of the separately formed closure 204, i.e. of the closure204 formed separately from the tubular wall 202. The separately formedclosure 204 includes a radially inner portion 212 and a radially outerflange 214 that, in an assembled state, is in physical contact with aradially inner surface 216 of an axial end 202 a of the tubular wall 202and extends from the radially inner portion 212 of the separately formedclosure 204 towards the opposite axial end 202 b of the tubular wall202.

The radially inner portion 212 includes a rotor supporting portion 222rotatably supporting an axial end portion 208 a of a rotor 208 by meansof a bearing 210 a. The rotor supporting portion 222 may be integrallyconnected to the flange 214 by means of a connection portion 226.

As shown in FIG. 2 , the rotor supporting portion 222 may include anannularly shaped circumferential wall 224 extending in the axialdirection A and an axial end wall 228 including a through hole 230configured to receive an axial end portion 208 a of the rotor 208therein. A bearing insertion opening 232 is formed at an axial end ofthe rotor supporting portion 222 opposite to the axial end wall 228.

In contrast to the first example embodiment shown in FIG. 1 , the axialend wall 228 of the rotor supporting portion 222 is connected to thecircumferential wall 224 thereof at an axial end portion opposite to theopposite axial end 202 b of the tubular wall 202, meaning that in anassembled state of the separately formed closure 204, the bearing 210 ais not accessible from the exterior of the housing 200. In this way, theaxial end wall 228 may serve as a protection means for the bearing 210 aagainst external factors such as moisture, dirt, or mechanical impacts.

In addition, different from the first example embodiment shown in FIG. 1, the connection portion 226 of the radially inner portion 212 isconnected to an axial end portion of the circumferential wall 224 facingthe opposite axial end 202 b of the tubular wall 202, i.e. opposite tothe axial end wall 228. Consequently, different from the connectionportion 126 of the first example embodiment, the connection portion 226of the separately formed closure 204 of the housing 200 according to thesecond example embodiment includes a substantially radially extendingportion 226-R and a substantially axially extending portion 226-A. Theaxially extending portion 226-A of the connection portion 226 and thecircumferential wall 224 of the rotor supporting portion 222 may besubstantially co-extensive in the axial direction A.

The circumferential wall 224 and the axially extending portion 226-A ofthe connection portion 226 may form a biasing member having a V-shapedcross sectional configuration in a state in which the separately formedclosure 204 is separated from the tubular wall 202, meaning that thecircumferential wall 224 and the axially extending portion 226-A of theconnection portion 226 are connected to each other only at an axial end225 opposite to the axial end wall 228. The biasing member may becompressed by a radially inward force, e.g. by a radially inward forceapplied onto the separately formed closure 204 when inserting theseparately formed closure 204 into the tubular wall 202. By means ofthis force, the circumferential wall 224 and the axially extendingportion 226-A of the connection portion 226 may be brought into mutualphysical contact along a contact surface 227 of the circumferential wall224. Consequently, in the assembled state of the separately formedclosure 204, the biasing member is compressed and may thus exert a forcein a radially outward direction onto the radially inner surface 216 ofthe tubular wall 202 by means of the flange 214, thereby enhancing thepress fit engagement force as compared to the first example embodiment.

In FIG. 3 , a housing for an electric motor according to a third exampleembodiment is shown. The third example embodiment will be described onlyinasmuch as it differs from the first example embodiment shown in FIG. 1. In FIG. 3 , parts corresponding to parts of the housing 100 shown inFIG. 1 will be denoted by the same reference numerals, however, enhancedby the number 200.

The housing 300 shown in FIG. 3 differs from the housing 100 accordingto the first example embodiment in view of the configuration of theclosure 306 integrally formed with the tubular wall 302.

Similar to the housing 100 according to the first example embodiment,the integrally formed closure 306 also includes a rotor supportingportion 334 configured to rotatably support a rotor 308 by means of abearing 310 b. The rotor supporting portion 334 includes acircumferential wall 336 as well as an axial end wall 338 including athrough hole 340 configured to receive an axial end portion 308 b of therotor 308 therein. Opposite to the axial end wall 338 a bearinginsertion opening 342 is provided.

Different from the first example embodiment, the axial end wall 338 isprovided at an axial end of the rotor supporting portion 334 opposite tothe opposite axial end 302 a of the tubular wall 302, meaning that in anassembled state the bearing 310 b is not accessible from the exterior ofthe housing 300. In this way, the axial end wall 338 may serve as aprotection means for the bearing 310 b against external factors such asmoisture, dirt, or mechanical impacts.

In FIG. 4 , a housing for an electric motor according to a fourthexample embodiment is shown. The fourth example embodiment will bedescribed only inasmuch as it differs from the first example embodimentshown in FIG. 1 . In FIG. 4 , parts corresponding to parts of thehousing 100 shown in FIG. 1 will be denoted by the same referencenumerals, however, enhanced by the number 300.

The housing 400 shown in FIG. 4 includes, similar to the housing 100shown in FIG. 1 , a tubular wall 402 with a closure 404 formedseparately from the tubular wall 402 and a closure 406 formed integrallywith the tubular wall 402. The housing 400 shown in FIG. 4 differs fromthe housing 100 according to the first example embodiment in view ofboth the separately formed closure 404 and the integrally formed closure406. More specifically, the housing 400 according to the fourth exampleembodiment includes a separately formed closure 406 according to thesecond example embodiment shown in FIG. 2 and an integrally formedclosure 406 according to the third example embodiment shown in FIG. 3 .The respective closures have been described above in detail. Therefore,a detailed description of the closures 404 and 406 of the housing 400according to the fourth example embodiment will be omitted here.

The housings 100 to 400 described above may be employed in an electricmotor including a stator fixedly mounted inside of a housing 100 to 400and configured to generate a time-varying magnetic field. The rotorsshown in the figures may be at least temporarily or even permanentlymagnetized and may be rotatable by means of a magnetic interaction withthe time-varying magnetic field generated by the stator.

An exemplary electric motor 101 is indicated in FIG. 1 . This motor 101includes the previously discussed housing 100, the rotor 108, and astator 109 mounted in the interior space 120 of the housing 100.

An electric motor of this kind may be employed in an electric pumpconfigured to convey, e.g. a service liquid in a vehicle such aslubricating oil or a coolant.

In the following, various examples of the present disclosure will bedescribed.

Example 1 is a housing for an electric motor. The housing includes: atubular wall extending in an axial direction of the housing, andclosures positioned at opposite axial ends of the tubular wall andconfigured to rotatably support opposite axial end portions of a rotor.At least one of the closures is formed separately from the tubular walland includes a radially inner portion and a radially outer flange that,in an assembled state, is in physical contact with a radially innersurface of the tubular wall and extends from the radially inner portionof the separately formed closure towards the opposite axial end of thetubular wall.

In Example 2, the subject matter of Example 1 can optionally furtherinclude that the radially inner portion of the separately formed closureincludes a rotor supporting portion configured to rotatably support anaxial end portion of a rotor by means of a bearing. The rotor supportingportion may include an annularly shaped circumferential wall extendingin the axial direction of the housing and configured to receive abearing therein for rotatably supporting an axial end portion of therotor.

In Example 3, the subject matter of Example 2 can optionally furtherinclude that the rotor supporting portion of the separately formedclosure includes an axial end wall including a through hole extending inthe axial direction and configured to receive the rotor therein. Theaxial end wall may be formed at an axial end of the circumferential wallfacing the respective other closure or opposite to the respective otherclosure.

In Example 4, the subject matter of Example 3 can optionally furtherinclude that the rotor supporting portion of the separately formedclosure includes a bearing insertion opening at an axial end thereofopposite to the axial end wall.

In Example 5, the subject matter of any one of Examples 3 or 4 canoptionally further include that the radially inner portion includes aconnection portion integrally connecting the flange with an axial endportion of the circumferential wall opposite to the axial end wall.

In Example 6, the subject matter of any one of Examples 3 to 5 canoptionally further include that the through hole is provided with anon-rotationally symmetric shape such as a triangular or polygonalshape.

In Example 7, the subject matter of any one of Examples 1 to 6 canoptionally further include that one of the closures is integrally formedwith the tubular wall.

In Example 8, the subject matter of Example 7 can optionally furtherinclude that the closure integrally formed with the tubular wallincludes a rotor supporting portion configured to rotatably support anaxial end portion of a rotor by means of a bearing. The rotor supportingportion of the integrally formed closure may include an annularly shapedcircumferential wall extending in the axial direction and configured toreceive a bearing therein for rotatably supporting an axial end portionof the rotor.

In Example 9, the subject matter of Example 8 can optionally furtherinclude that the rotor supporting portion of the integrally formedclosure includes an axial end wall including a through hole extending inthe axial direction and configured to receive the rotor therein. Theaxial end wall may be formed at an axial end of the circumferential wallfacing or opposite to the closure separately formed from the tubularwall.

In Example 10, the subject matter of Example 9 can optionally furtherinclude that the rotor supporting portion of the integrally formedclosure includes a bearing insertion opening at an axial end thereofopposite to the axial end wall.

In Example 11, the subject matter of any one of Examples 9 or 10 canoptionally further include that the through hole is provided with anon-rotationally symmetric shape such as a triangular or polygonalshape.

In Example 12, the subject matter of any one of Examples 1 to 11 canoptionally further include that the closure separately formed from thetubular wall is press fit into the interior of an axial end portion ofthe tubular wall.

In Example 13, the subject matter of any one of Examples 1 to 12 canoptionally further include that the inner surface of the tubular wallincludes a positioner configured to be brought into physical contactwith the flange of the separately formed closure.

In Example 14, the subject matter of Example 13 can optionally furtherinclude that the positioner is configured as or includes a stepextending in the circumferential direction of the tubular wall andprotruding radially inwardly.

In Example 15, the subject matter of any one of Examples 1 to 14 canoptionally further include that at least one of the closures and/or thetubular wall is/are formed by press forming and/or deep drawing.

Example 16 is an electric motor including: a housing of any one ofExamples 1 to 15, a stator fixedly mounted inside of the housing andconfigured to generate a time-varying magnetic field, and a rotorrotatably mounted inside of the housing and configured to be rotated byan interaction with the time-varying magnetic field generated by thestator.

Features of the above-described preferred example embodiments and themodifications thereof may be combined appropriately as long as noconflict arises.

While example embodiments of the present disclosure have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present disclosure. The scope of the presentdisclosure, therefore, is to be determined solely by the followingclaims.

What is claimed is:
 1. An electric motor comprising: a housing includinga tubular wall extending in an axial direction of the housing andclosures positioned at opposite axial ends of the tubular wall; a statorfixedly mounted inside of the housing; a rotor rotatably mounted insideof the housing; a bearing rotatably supporting the rotor; wherein atleast one of the closures includes a rotor supporting portion thatincludes a through hole to receive a portion of the rotor; and thethrough hole is provided with a non-rotationally symmetric shape.
 2. Theelectric motor of claim 1, wherein the non-rotationally symmetric shapeis defined by a closed shape including at least three or more straightsides; and a radius of an inscribed circle of closed shape of thethrough hole is larger than a radius of the portion of the rotorreceived in the through hole.
 3. The electric motor of claim 2, whereinthe closures at both axial ends of the tubular wall include the rotorsupporting portions having the closed shape including at least three ormore straight sides.
 4. The electric motor of claim 1, wherein at leastone of the closures is separate from the tubular wall, and includes aradially inner portion which includes the rotor supporting portion and aradially outer flange which is in physical contact with a radially innersurface of the tubular wall and extends from the radially inner portionof the closure towards an opposite axial end of the tubular wall.
 5. Theelectric motor of claim 4, wherein the radially inner portion of the atleast one of the closures which is separate from the tubular wallincludes: a rotor supporting portion including an annularly shapedcircumferential wall extending in the axial direction; an axial end wallincluding the through hole; a bearing insertion opening at an axial endthereof opposite to the axial end wall; the axial end wall is providedat an end on an outer side of the housing with respect to the annularlyshaped circumferential wall; and the bearing insertion opening isprovided at the axial end on an inner side of the housing with respectto the annularly shaped circumferential wall.
 6. The electric motor ofclaim 5, wherein the radially inner portion includes a connectionportion integrally connecting the radially outer flange with an axialend portion of the circumferential wall opposite to the axial end wall;the connection portion includes a substantially radially extendingportion and a substantially axially extending portion; the substantiallyradially extending portion connects the radially outer flange andextends radially; and the substantially axially extending portionconnects the substantially axially extending portion and the annularlyshaped circumferential wall, and extends axially.
 7. The electric motorof claim 4, wherein the radially inner surface of the tubular wallincludes a positioner to be brought into physical contact with theradially outer flange of the at least one of the closures which isseparate from the tubular wall; the positioner includes a step extendingin the circumferential direction of the tubular wall and protrudingradially inwardly.
 8. The electric motor of claim 1, wherein one of theclosures is integral with the tubular wall.
 9. The electric motor ofclaim 8, wherein the rotor supporting portion of the one of the closuresintegral with the tubular wall includes a circumferential wall extendingin the axial direction to receive the bearing therein to rotatablysupport an axial end portion of the rotor.
 10. The electric motor ofclaim 9, wherein the rotor supporting portion of the one of the closuresintegral with the tubular wall includes an axial end wall including thethrough hole, and a bearing insertion opening into which the bearing isinserted; the axial end wall is located at an axial end on an inner sideof the housing with respect to the circumferential wall; and the bearinginsertion opening is located at an axial end on an outer side of thehousing with respect to the circumferential wall.
 11. An electric motorcomprising: a housing including a tubular wall extending in an axialdirection of the housing and closures positioned at opposite axial endsof the tubular wall; a stator fixedly mounted inside of the housing; arotor rotatably mounted inside of the housing; a bearing rotatablysupporting the rotor; wherein at least one of the closures includes arotor supporting portion that includes a through hole to receive aportion of the rotor; and the through hole is defined by a closed shapeincluding at least three or more straight sides.
 12. The electric motorof claim 11, wherein the closures at both axial ends of the tubular wallinclude the rotor supporting portions having the closed shape includingat least three or more straight sides.
 13. The electric motor of claim11, wherein the through hole is provided with a non-rotationallysymmetric shape.
 14. The electric motor of claim 11, wherein at leastone of the closures is separate from the tubular wall, and includes aradially inner portion which includes the rotor supporting portion and aradially outer flange which is in physical contact with a radially innersurface of the tubular wall and extends from the radially inner portionof the closure towards an opposite axial end of the tubular wall. 15.The electric motor of claim 14, wherein the radially inner portion ofthe at least one of the closures which is separate from the tubular wallincludes: a rotor supporting portion including an annularly shapedcircumferential wall extending in the axial direction; an axial end wallincluding the through hole; a bearing insertion opening at an axial endthereof opposite to the axial end wall; the axial end wall is providedat an end on an outer side of the housing with respect to the annularlyshaped circumferential wall; and the bearing insertion opening isprovided at the axial end on an inner side of the housing with respectto the annularly shaped circumferential wall.
 16. The electric motor ofclaim 15, wherein the radially inner portion includes a connectionportion integrally connecting the radially outer flange with an axialend portion of the circumferential wall opposite to the axial end wall;the connection portion includes a substantially radially extendingportion and a substantially axially extending portion; the substantiallyradially extending portion connects the radially outer flange andextends radially; and the substantially axially extending portionconnects the substantially axially extending portion and the annularlyshaped circumferential wall, and extends axially.
 17. The electric motorof claim 14, wherein the radially inner surface of the tubular wallincludes a positioner to be brought into physical contact with theradially outer flange of the at least one of the closures which isseparate from the tubular wall; the positioner includes a step extendingin the circumferential direction of the tubular wall and protrudingradially inwardly.
 18. The electric motor of claim 11, wherein one ofthe closures is integral with the tubular wall.
 19. The electric motorof claim 18, wherein the rotor supporting portion of the one of theclosures integral with the tubular wall includes a circumferential wallextending in the axial direction to receive the bearing therein torotatably support an axial end portion of the rotor.
 20. The electricmotor of claim 19, wherein the rotor supporting portion of the one ofthe closures integral with the tubular wall includes an axial end wallincluding the through hole, and a bearing insertion opening into whichthe bearing is inserted; the axial end wall is located at an axial endon an inner side of the housing with respect to the circumferentialwall; and the bearing insertion opening is located at an axial end on anouter side of the housing with respect to the circumferential wall.